1. Field of the Invention
The present invention relates to data conversion of a storage medium, and more particularly to a data conversion method of a specific area of a storage medium, which is associated with data in the storage medium, an apparatus and a program.
2. Description of the Related Art
Methods for converting data in a storage medium in a decryptable format in anticipation of, e.g. a theft of a storage medium such as a hard disk, include a method of encrypting data by using an encryption algorism or the like. The encryption generally falls into two categories, i.e. file encryption and disk encryption.
In the file encryption, encryption is executed in units of a file or a folder in an application layer on an operating system (OS).
On the other hand, in the disk encryption, encryption is executed in units of a sector at a lower level than a file system. In general, the entire disk is encrypted. The disk encryption is more advantageous than the file encryption in the case where the data in the disk is to be encrypted regardless of an operation user's intension, or in the case where the processing speed is taken into account.    Patent document 1: Jpn. Pat. Appln. KOKAI Publication No. 2005-172866, and    Patent document 2: Jpn. Pat. Appln. KOKAI Publication No. 2006-033326.
As described above, in the conventional disk encryption, the object of encryption is the entire disk. Consequently, a long time (about several hours) is needed when initial encryption is executed from a non-encrypted state, and in a case where the disk has a defect, there is such a problem that the initial encryption fails to be finished. In addition, while the initial encryption is being executed, there is such inconvenience that the associated computer terminal is not usable for work.
As a measure for avoiding such problems, it is thinkable that only a necessary region, which is used by data in the storage medium that meets a specific target condition, is set as an object of encryption while making use of the advantage of the disk encryption, for example, by encrypting only an actually used region. However, since the disk encryption is executed in the process at the lower level than the file system, at which level there is no concept of files, the conventional disk encryption is unable to selectively encrypt the region which is associated with data in the storage medium such as a file.